The present invention relates to a storage system for use in a computer system.
The data migration technology from a first storage system to a second storage system is described in JP-A-2000-187608.
In JP-A-2000-187608, once connected with a host computer, the second storage system issues a read request to the first storage system so that data in the first storage system is copied into the second storage system. The second storage system is provided with a copy pointer for recording the completion level of data copying to indicate the progress of data migration.
During such data migration, an I/O request issued by the host computer is accepted by the second storage system. In an exemplary case where a read request is issued from the host computer during data migration, the second storage system refers to the copy pointer to see whether data in the request has already be copied to the second storage system. If so, the second storage system forwards the data to the host computer. If not, the second storage system reads the requested data from the first storage system for transfer to the host computer.